Epidemiological Approach to the Paleopathological Diagnosis of Leprosy

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 115:380–387 (2001)

Jesper L. Boldsen*

Anthropological Data Base Odense University and Danish Center for Demographic Research, SDU-Odense University, DK 5000 Odense, Denmark

KEY WORDS sensitivity; speciﬁcity; simultaneous estimation; skeletal lesions; lepers institutions; cemeteries; Denmark

ABSTRACT In paleopathology it is usually assumed samples were scored for the presence of seven osteological that modern diagnostic criteria can be applied to infectious conditions indicating leprosy. For the osteological conditions, diseases in the past. However, as both the human species sensitivity varied from 0.36–0.80, and speciﬁcity from 0.58– and populations of pathogenic microorganisms undergo evo- 0.98. The frequency of leprosy in the three samples was: lutionary changes, this assumption is not always well- Odense (a lepers’ institution), 0.98, 95% CI 0.64–1.00; founded. To get valid estimates of the frequency (the point Malmo¨ (urban cemetery), 0.02, 95% CI 0.00–0.07; and Tirup prevalence at death) of leprosy in skeletal samples, sensitiv- (rural cemetery), 0.36, 95% CI 0.23–0.46. It is concluded that ity, speciﬁcity, and sample frequency must be estimated it is indeed possible to estimate disease frequencies without simultaneously. It is shown that more than three symptoms reference to modern standards, and that leprosy occurred must be evaluated in at least three samples in order to reach with widely differing frequencies in different segments of the estimates with well-described properties. The method is ap- Medieval population in southern Scandinavia. Am J Phys plied to three skeletal samples from Medieval Denmark; the Anthropol 115:380–387, 2001. © 2001 Wiley-Liss, Inc.

Leprosy was a dreaded disease in the Middle true spread of the disease. The cemetery of Sct. Ages. The clearly visible symptoms of advanced lep- Jørgensgård contains many more lepers than would romatous leprosy stigmatized the diseased. Special be a reflection of the population prevalence, and institutions were created in many places in Europe ordinary cemeteries would perhaps be lacking in to accommodate the victims of leprosy. The name of lepers as the victims had been selected out of the the disease actually reflects this institutionalization general population. However, before one can begin of the sufferers in several languages: German “Aus- to address questions about the processes related to satz” (excluded) and, in the Scandinavian lan- leprosy in the once-living population, it is necessary guages, “spedalskhed” (derived from the word hos- to go beyond the counting of leprous lesions. All pital). The bringing together of lepers in an symptoms (in this case, osteologically identifiable institution and the following burial of dead inmates leprosy-related lesions) have special epidemiological of the institutions in special cemeteries has permit- properties which can be described by specificity and ted research into Medieval leprosy. The first modern sensitivity. Generally, the specificity and sensitivity studies date back to the 19th century (Ehlers, 1898). of leprosy-related osteological conditions are un- This study was archaeologically and historically fol- known, and it is highly probable that they have lowed up by Richards (1960, 1977). It was Møller- changed over centuries with the coevolution of hu- Christensen (1951, 1953, 1961, 1963, 1978) who ini- mans and the bacterium causing leprosy. This paper tiated osteological research into Medieval leprosy. sets out to create methods (osteological and statisti- Andersen (1969, 1991) went on to analyze the diag- cal) to permit the simultaneous estimation of sensi- nostic process for leprosy in Medieval Denmark. Os- tivity and specificity of several osteological symp- teological studies have widened to include estima- toms of leprosy and the frequency of leprosy (the tion of the frequency of lepers in skeletal samples point prevalence of leprosy at death) in several skel- from lepers institutions and ordinary cemeteries etal samples. (Andersen, 1969; Boldsen, 1978; Bennike, 1985; Ar- cini, 1990, 1999; Arentoft, 1999). The frequency of leprous (or any other) lesions Grant sponsor: Danish Foundation for Basic Research. among excavated skeletons has very little bearing *Correspondence to: Jesper L. Boldsen, Anthropological Data Base on the processes of health and disease in the once- Odense University, SDU-Odense University, Campusvej 55, DK 5230 living population (Wood et al., 1992). The selection Odense M, Denmark. E-mail: [email protected] of lepers into lepers’ institutions (in Danish: Sct. Jørgensgård) makes it very difficult to study the Received 12 September 2000; accepted 30 April 2001.

© 2001 WILEY-LISS, INC. PALEOPATHOLOGICAL DIAGNOSIS OF LEPROSY 381 TABLE 1. Relationship between disease and symptom in It is obvious from the formulae listed above that relationship to leprosy knowledge about sensitivity and specificity is re- Leprosy quired to estimate the population prevalence of the Sumptom Yes No Total disease, and that the estimation of the probability that a person showing the symptom actually had the Yes Truly positive Falsely positive Positive No Falsely negative Truly negative Negative disease also requires information on population Total Sick Not sick All prevalence. It is likely that human populations have evolved through their interaction with populations of patho- MATERIALS AND METHODS gens like Mycobacterium leprae (the bacterium caus- Epidemiological background ing leprosy), and the pathogens are likely to have changed even more through interaction with specific Paleopathological diagnosis is in most ways simi- human populations. This means that diseases have lar to screening for diseases in modern society. The not retained the same clinical symptomatic image purpose of the exercise is both to estimate the prev- over centuries, and that sensitivities and specifici- alence of the disease in a given (sub)population and ties for specific symptoms have not remained un- to assess if a given individual suffers from the dis- changed. Therefore, in order to study the prevalence ease. In reality, no osteological symptom occurs only of leprosy in Medieval Denmark, specificities and among people with the disease, and no single symp- sensitivities for the symptoms involved must be es- tom is shown by all who suffered from the disease. timated based on Medieval data. Table 1 summarizes the basic relationship between Gold standards do not exist in modern epidemiol- disease (in this case leprosy) and any given symp- ogy, and the situation is even more difficult in pa- tom. leoepidemiology. This means that there is no terra Epidemiologically, a symptom is characterized by firma from which sensitivities and specificities can sensitivity (the probability of having the symptom, be estimated. However, if given that an individual had the disease) and specificity (the probability of not having the symptom, p ⅐ s Ͼ p ϩ 2 ⅐ s, (5) given that an individual did not have the disease). where p is the number of populations studied and s truly positive the number of symptoms used to analyze the dis- sensitivity ϭ sick ease, then it is possible to estimate sensitivities and specificities of the s different symptoms, as well as ϭ p͑positive͉sick͒ (1) the p different population prevalences, and to test truly negative the goodness of fit of the model to the observations. specificity ϭ In the present analyses, p ϭ 3 and s ϭ 7, so the not sick number of degrees of freedom (df) for the goodness of ϭ p͑negative͉not sick͒ (2) fit test becomes four: Following this, an observable (osteological) condi- df ϭ p ⅐ s Ϫ ͑p ϩ 2 ⅐ s͒ ϭ 21 Ϫ 17 ϭ 4 (6) tion is a symptom of a given disease if sensitivity is larger than one minus specificity. In other words, This line of reasoning makes it possible to estimate the probability of having the condition is larger the epidemiological properties of paleopathological among people with the disease than among people symptoms and the population prevalence of the dis- without that particular disease. This does not imply ease (leprosy) under the assumption of indepen- that the majority of people showing the symptom dence among the expression of the different symp- actually have the disease. In paleopathology, and in toms among people without the disease. modern screening programs, the only observable Samples statistic is the frequency of people showing the symptom. However, using sensitivity and specificity Three samples of skeletons from Medieval Den- it is possible to estimate the population prevalence mark have yielded data for the analyses in this (frequency of lepers in the skeletal sample p(sick)) paper: Sct. Jørgen in Odense, Kvarteret St. Jo¨rgen from the frequency of the symptom (p(positive)): in Malmo¨ (Swedish since 1660), and Tirup. Two of the cemeteries (Odense and Malmo¨) have been as- p͑positive͒ Ϫ ͑1 Ϫ specificity͒ p͑sick͒ ϭ (3) sociated with lepers’ hospitals (the so-called Sct. Jør- sensitivity Ϫ ͑1 Ϫ specificity͒ gensgård; Arentoft, 1999), and the third is a rural And once the population prevalence of the disease parish cemetery (Kieffer-Olsen et al., 1986). The (p(sick)) has been estimated from an equation like locations of the three cemeteries are indicated in (3), it is possible to estimate the predictive value for Figure 1. The Odense and Tirup samples are part of the symptom in a given population (P(sick͉symptom)): the collections of the Anthropological Data Base Odense University (ADBOU), and the Malmo¨ sam- ⅐ ͑ ͒ sensitivity p sick ple is temporarily being kept in ADBOU for regis- p͑sick symptom͒ ϭ (4) p͑symptom͒ tration and analysis. 382 J.L. BOLDSEN

Fig. 1. Denmark in Middle Ages, including provinces of Skåne, Halland, and Blekinge (now part of Sweden) and of South Slesvig (now in Germany). Sites are indicated by name of town or village where site is situated: Odense, Sct. Jørgen in Odense; Malmo¨, Kvartetet St. Jo¨ rgen in Malmo¨; and Tirup.

Sct. Jørgen in Odense was excavated by Odense yielded data on 635 individuals aged 15 or more at Bys Museer in 1979–1981 (Jensen and Tkocz, 1983). death. The excavation uncovered the foundation of a The cemetery in Kvarteret St. Jo¨rgen in Malmo¨ church and the remains of several secular buildings has been interpreted as that of a lepers institution belonging to the Sct. Jørgensgård. The cemetery was like the Odense cemetery. However, the written totally excavated, yielding evidence for 1,507 buri- sources linking this Malmo¨ cemetery with a lepers’ als: of these, 924 skeletons were found in recognized hospital are not clear. The cemetery was totally ex- graves, and 239 skulls were collected without asso- cavated by Malmo¨ Museum in 1990–1991, and the ciated postcranial bones. Many of the skeletons osteological material recovered is presently being show gross deformations compatible with advanced examined and recorded primarily in ADBOU. Ap- leprosy. The skeletons of the Odense sample were proximately 1,600 graves were excavated, and 10 m3 primarily examined for this study. The burials at of scattered human skeletal remains were recov- Sct. Jørgen in Odense are dated to a period from the ered. The cemetery and thus the burials date to the middle of the 13th to the middle of the 17th century period from around AD 1320–1520 (Billberg, per- AD. During this period, the function of the cemetery sonal communication). Data for the analyses in this changed from serving the inmates of the hospital paper were only extracted from skeletons found in (i.e., the lepers) to serving as a general cemetery of graves. A total of 200 skeletons of persons aged 15 or the poor people of Odense (Arentoft, 1999). A certain more at death yielded data for the analyses here. level of disagreement exists among archaeologists as The third cemetery, Tirup, has provided the skel- to the continuity of burials in the cemetery. The etal remains of the best-known Medieval village primary investigator sees evidence for burials tak- population in Northern Europe. Tirup was exca- ing place more or less continuously (Arentoft, 1999), vated in 1984. Remains of 620 human beings were whereas the leading Danish expert on Medieval found and have subsequently been analyzed demo- burial customs finds evidence of a hiatus of burials graphically and epidemiologically in numerous ways between around AD 1400–1550 (Kieffer-Olsen, (Kieffer-Olsen et al., 1986; Boldsen, 1988, a,b, 1999). 1993). The cemetery of Sct. Jørgen in Odense has The cemetery is dated to the period from the middle PALEOPATHOLOGICAL DIAGNOSIS OF LEPROSY 383 of the 12th to the middle of the 14th century AD vitam destruction of the alveolar process, i.e., the (Kieffer-Olsen, 1993). The registration of leprosy- prosthion has retreated above a straight line con- related osteological changes in the Tirup sample is necting the post prominent point on the alveolar part of the ongoing research into the health, well- process between the lateral incisor and the canine in being, and mortality of the Tirup population. In both sides of the upper jaw. spite of the numerous analyses of health-related variations in the Tirup sample, it is only now in the Palate process of being registered for symptoms of leprosy. A total of 61 skeletons of individuals aged 15 or more The location is the palatine process of the maxilla. at death yielded data for the analyses in this paper. Scores were 1) normal palate; and 2) pitted or perforated palate, over one half of the palate is macro- Osteological methods porous (i.e., covered by densely packed small holes The focus of this paper is to estimate the preva- with a diameter of over 0.5 mm), and/or the palate is perforated in one or more locations by holes measur- lence of leprosy at death in cemetery samples of ϫ skeletons. To be able to collect large data sets for the ing at least 2 2 mm. relevant variables quickly, a short form and a man- ual for the use of the form were developed. Prelim- Subperiosteal exosteoses on fibula inary analyses showed that the variables primarily The location is the middle part of the mesial face analyzed were virtually independent of age at death of fibula, and the surface of the interosseous crest of and sex of the skeleton. As a consequence of this, sex fibula. Scores were 1) normal smooth surface of the was assessed on a seven-point scale, and age was bone in the area; and 2) more than two rounded, estimated subjectively, primarily following criteria pointed, or even jagged exosteoses are found in the described by the Workshop of European Anthropol- area, the exosteoses must be at least 2 mm long, and ogists (1980). Osteological changes indicative of lep- the surface of the exosteoses must be wood-like to rosy were recorded in seven different locations on qualify for this scoring. Usually, the subperiosteal the skeleton: 1) the edge of the nasal aperture, 2) the exosteoses first appear along the interosseous crest anterior nasal spine, 3) the alveolar process on the of fibula. premaxilla, 4) the palate, 5) subperiosteal exosteoses on fibula, 6) porotic hyperosteosis on the fibula, Porous hyperostosis of the fibula and 7) the fifth metetarsal. Although some of the symptoms can best be described by a multistage Location was the middle part of the of the mesial sequence of changes, for the purpose of the present face of fibula, and the surface of the interosseous analyses they have all been dichotomized to 1) ab- crest. Scores were 1) normal bone; and 2) distinct sent and 2) present. In the coding of data, zero was “swelling” of the bone surface: the surface has more used to indicate unobservable. or less prominent bumps which are smooth, and small (or large) drainage holes are also present in Edge of the nasal aperture the area. The location is the vertical part of the edges of the nasal aperture in both sides, from the most inferior Fifth metatarsal point on the nasal-maxillary suture to approximately 1 cm lateral to the anterior nasal spine. Location was the metatarsal bone of the little Scores were 1) normal edge of the nasal aperture, (fifth) toe. Scores were 1) normal bone; and 2) any i.e., sharp edges; and 2) rounded edges of the nasal changes of the bone from mild but distinct periosteal aperture, i.e., at least 0.5 cm of this edge is rounded. reactions to grossly deformed bone. Anterior nasal spine Statistical methods The location is the most anterior point of the me- The problem outlined above can be solved by esti- dia-sagittal plane of the nasal aperture, where the mating the values of 17 parameters. Three parame- ␲ ϭ two lateral edges meet. Scores were 1) the spine is ters ( i,i 1, 2, 3) describe the frequency (point pointed; and 2) missing spine, and the bone where prevalence at death among adult people in the ith ␶ ϭ the spine was situated is well-preserved and well- sample) of leprosy; seven parameters ( j,j 1,...,7) rounded. If there is a slight possibility that the ab- describe the probability of having the jth symptom, ␶ sence of the spine and the rounding the bone in the given that the individual had the disease ( j is the area is due to postmortem degradation, a zero is sensitivity of the jth symptom); and seven parame- scored. ␾ ϭ ters ( j,j 1, . . ., 7) describe the probability of not having the jth symptom, given that the individual Alveolar process of the premaxilla ␾ did not have the disease ( j is the specificity of the The location is the anterior part of the premaxilla, jth symptom). All 17 parameters are constrained to basically the bone around the four upper incisors. the interval ]0;1[. The log-likelihood function (LL) Scores were 1) normal alveolar process; and 2) intra for the 17 parameters has the following form: 384 J.L. BOLDSEN

TABLE 2. Numbers of affected and unaffected skeletons for each of the seven symptoms and each of the three samples, i.e., the raw data used for the analyses Odense Malmo¨ Tirup Sum ␹2 (df ϭ 2) P Edge of the nose Unaffected 133 113 23 269 Affected 250 20 15 285 102.08 Ͻ0.001 Sum 383 133 38 554 Anterior nasal spine Unaffected 130 121 27 278 Affected 119 4 6 129 79.46 Ͻ0.001 Sum 249 125 33 407 Alveolar process of the premaxilla Unaffected 227 142 33 402 Affected 179 3 8 190 89.76 Ͻ0.001 Sum 406 145 41 Palate Unaffected 138 115 39 292 Affected 294 40 17 351 96.67 Ͻ0.001 Sum 432 155 56 643 Subperiosteal exosteoses on ﬁbula Unaffected 76 91 18 185 Affected 294 67 27 388 70.87 Ͻ0.001 Sum 370 158 45 573 Porous hyperosteosis on ﬁbula Unaffected 227 146 34 407 Affected 125 12 9 146 44.46 Ͻ0.001 Sum 352 158 43 553 Fifth metatars Unaffected 117 114 22 253 Affected 121 16 10 147 54.16 Ͻ0.001 Sum 238 130 32 400

3 7 2 TABLE 3. Epidemiological properties of paleopathological ϭ ͸ ͸ ͸ ͓ ⅐ ͑␲ ⅐ ␶ ϩ ͑ Ϫ ␲ ͒ ⅐ symptoms of leprosy LL ni,j,k ln ak i j 1 i iϭ1 jϭ1 kϭ1 95% ͑ Ϫ ␾ ͒͒ ϩ ͑ Ϫ ͒ ⅐ ͑␲ ⅐ ͑ Ϫ ␶ ͒ ϩ ͑ Ϫ ␲ ͒ ⅐ ␾ ͔͒ conﬁdence 1 j 1 ak i 1 j 1 i j interval (7) Symptom Estimate SE Lower Upper

Here in Equation (7), ni,j,k is the number of skeletons Edge of the nose from the ith sample who for the jth symptom are Sensitivity 0.662 0.108 0.653 1.000 ϭ ϭ Specificity 0.854 0.021 0.800 0.887 either positive (k 1) or negative (k 2); and ak is Spina nasalis anterior ϭ ϭ an indicator variable, with a1 1 and a2 0, dis- Sensitivity 0.486 0.082 0.410 0.731 tinguishing between positive and negative observa- Specificity 0.976 0.012 0.955 1.000 Alveolar process tions of the symptom given. Sensitivity 0.449 0.091 0.441 0.732 The parameters of this model were found by Specificity 0.985 0.016 0.922 1.000 means of constrained nonlinear regression, using Palate the program package SPSS. This procedure implies Sensitivity 0.688 0.053 0.600 0.826 Specificity 0.757 0.076 0.742 1.000 fitting the parameter values by means of the least Subperiosteal exosteoses squares method. The standard errors and 95% con- Sensitivity 0.802 0.071 0.795 1.000 fidence intervals are found through bootstrapping. Specificity 0.580 0.024 0.500 0.604 Porous hyperosteosis RESULTS Sensitivity 0.361 0.066 0.355 0.572 Specificity 0.927 0.021 0.855 0.945 The observed numbers of skeletons with or with- Fifth metatars Sensitivity 0.516 0.096 0.508 0.842 out each of the seven symptoms and from each of the Specificity 0.881 0.025 0.800 0.907 three populations are summarized in Table 2. It appears that there are great differences in frequencies of affected skeletons in the three populations. nonlinear, so the fit might be much more sensitive to All the differences are statistically significant, and changes in one direction than to changes in the in all cases the frequency of affected skeletons was opposite direction. In cases like this, the likelihood largest in the Odense sample, followed by the Tirup function is far from symmetrical, leading to skewed and then the Malmo¨ sample. confidence intervals. For most symptoms, specifici- The results from fitting the model specified in ties are higher than sensitivities (Table 3), and as is Equation (7) are given in Tables 3 and 4. Generally always the case with screening tests (symptoms) the confidence intervals are rather skewed. This is like these, the two characteristic statistics (specific- probably a reflection of the fact that the model is ity and sensitivity) are negatively correlated (r ϭ PALEOPATHOLOGICAL DIAGNOSIS OF LEPROSY 385 TABLE 4. Estimates for point prevalence (frequency) of leprosy skeletons with clear evidence of leprosy in the cem- at death in each of the three analyzed populations etery of Sct. Mikkel has created the impression that 95% this cemetery also served the lepers’ hospital (Bold- confidence sen, 1978; Arentoft, 1999). interval In the light of this widespread assumption, the Site Estimate SE Lower Upper finding of a high prevalence of leprosy in a rural Odense Sct. Jr͞gen 0.982 0.111 0.643 1.000 parish cemetery (Tirup) and the virtual absence of Kvarteret St. Jo¨rgen, Malmo¨ 0.016 0.018 0.000 0.066 leprosy in a Sct. Jørgen cemetery (Malmo¨) are quite Tirup 0.356 0.108 0.225 0.456 unexpected and force a new interpretation of the epidemiology of the disease in Medieval Denmark. The sample from Sct. Jørgen in Odense is the only Ϫ0.89, P ϭ 0.006). If the symptoms of either the one where truly horrific changes due to leprosy are nasal spine, the alveolar processes, or porotic hyper- seen. This, in combination with the fact that the osteosis are seen in more than approximately 10% of prevalence of leprosy was close to 100%, demon- the skeletons of a population, it can be assumed that strates the selective character of the cemetery and at least some of the members of the once-living pop- the community it served. This is well in agreement ulation suffered from leprosy. This a reflection of the with general hypotheses about the structure and fact that specificity is higher than 0.9 for both symp- function of Sct. Jørgensgårde (Møller-Christensen, toms. 1951; Arentoft, 1999). The Medieval diagnosis of Based on the estimates of the prevalence of lep- leprosy focused very much on facial symptoms rosy in the three populations (Table 4), it seems safe (Andersen, 1969). The (semi)visible facial symptom to conclude that at least two thirds of the people of the nasal spine occurs around four times as fre- buried in the cemetery of Sct. Jørgen in Odense quently in the Odense sample as in the Tirup sam- suffered from leprosy. On the other end of the spec- ple, whereas the also (semi)visible symptom of the trum, it can be concluded than no more than 10% of fifth metatarsal is only twice as frequent in Odense. the people buried in the cemetery in Kvarteret St. This fact indicates that people with facial symptoms Jo¨rgen in Malmo¨ suffered from leprosy. For the were actively selected into the Odense sample. Con- third population, Tirup, thought to represent the sequently, it appears that referal to the lepers’ in- general rural population of the 12th to 14th centu- stitution in Odense did actually follow the Medieval ries, there is unequivocal evidence both for leprosy diagnostic criteria described by Andersen (1969). and for people without leprosy. Between one quarter Arentoft (1999) lists the St. Jo¨rgen cemetery in and one half of the people buried in Tirup suffered Malmo¨ as belonging to a Sct. Jørgensgård. Clearly, from leprosy. the people buried in this cemetery were not subject DISCUSSION to the same type of selection as those buried in the Odense Sct. Jørgen cemetery. The Malmo¨ cemetery The analyses presented here are focussed on the was founded later than the Odense cemetery, and in population level. The aim has been to estimate pop- accordance with the interpretation by Kieffer-Olsen ulation specific frequencies of leprosy and to de- (1993) of the burial pattern in Odense, most of the scribe the epidemiological properties of the symp- burials in Malmo¨ were made in a period when there toms of leprosy in Medieval Denmark. This means were none in the Odense cemetery. By the middle of that no attempts have been made to determine the 16th century, leprosy had disappeared from whether or not any given individual skeleton came Denmark, prevailing in Scandinavia only in western from a person who suffered from leprosy. However, Norway. It is likely that the absence of leprosy in using the estimates of sensitivity and specificity for Malmo¨ is due to the decline of the epidemic in the each of the seven symptoms (Table 3) and the esti- late Middle Ages. On the other hand, it is also pos- mates population point prevalences of leprosy at sible that the lepers from Malmo¨ were selected out of death (Table 4) it is possible to estimate the predic- the population actually buried in the St. Jo¨rgen cem- tive value of any symptom in each of the three sam- etery and institutionalized in an as yet unknown ples by applying formula (4). These estimates are lepers’ hospital in or close to Malmo¨. However, if this the closest it is possible to come to individual diag- were the case, selection in the city of Malmo¨ must noses, but they are probabilistic statements. In fact, have been much stronger than in the village of absolute statements about individual disease status Tirup, and it must have followed another set of are beyond what can be reached by palaeopathologi- criteria than that used for selecting people into the cal analysis. Odense cemetery. Leprosy is probably the most studied specific dis- There are no skeletons in the Tirup sample show- ease in the Scandinavian Middle Ages (Møller- ing comprehensive leprosy-related malformations. Christensen, 1978; Arcini, 1999; Arentoft, 1999). It In fact, the finding of symptoms of leprosy in high has often been assumed that lepers were (nearly) frequencies came as a great surprise for those study- exclusively found in cemeteries belonging to the spe- ing the Tirup skeletons. Tirup has always been in- cial lepers’ hospitals, e.g., Sct. Jørgensgårde. This terpreted as representing the general rural popula- assumption has been so strong that the finding of tion of the middle two centuries of the Middle Ages. 386 J.L. BOLDSEN

TABLE 5. Test for effect on age at death from absence (Ϫ) or presence (ϩ) of each of the seven symptoms in the odense sample1 Edge of the Alveolar Subperiosteal Porous Fifth nose Nasal spine process Palate exosteoses hyperosteosis metatars ϪϩϪϩϪϩϪϩϪϩϪϩϪϩ n 115 220 114 110 205 150 124 255 54 285 212 121 105 118 x៮ 30.0 26.6 29.7 26.7 29.1 26.2 29.6 27.1 33.4 28.0 29.8 27.4 32.7 27.3 SD 8.7 10.1 9.1 11.6 8.7 10.9 9.4 10.1 10.2 7.5 8.7 7.3 8.2 7.2 t Ϫ3.09 Ϫ2.12 Ϫ2.73 Ϫ2.42 Ϫ4.57 Ϫ2.53 Ϫ5.27 p Ϫ0.002 0.035 0.007 0.016 0.000 0.012 0.000

1 n, number of observations; x៮, average age; SD, standard deviation; t, Student’s t-test statistic; p, test probability.

The finding of a high prevalence of leprosy in this Paleopathology needs to move into a truly epide- sample indicates that a relatively high proportion of miological stage. If the dynamic relationship be- the rural Danish population was in fact affected by tween pathogens and human populations is not leprosy in the 13th century AD. The methodology taken into consideration, serious bias is likely to used in this paper to analyze leprosy epidemiologi- result. The present paper represents a first step in cally, based on minor anatomical changes, has made the direction of understanding the epidemiological it possible to study the spread of the disease in the processes involved in Medieval leprosy. Point prev- population in general and not only in the tiny mi- alence of the disease at the time of death (and thus nority of institutionalized people forming the previ- frequency of disease in a skeletal sample) is not very ously visible tip of the iceberg. informative about processes in the once-living pop- It is possible to check some of the assumptions ulation. It is generally claimed that leprosy is not a behind the model. First of all, the model fits the deadly disease (Bryceson and Pfaltzgraff, 1990). If data. The goodness of fit test gives ␹2 ϭ 4.40, df ϭ 4, this were actually true, then the prevalence of lep- P Ն 0.3. But that is no proof that it provides a rosy at death should represent the prevalence in the realistic image of the epidemiological properties of once-living population. However, this is highly un- the symptoms and the prevalences of leprosy in the likely. In the Odense sample, severity of the disease different communities. Using the finding that virtu- (as measured by presence of symptoms) is associated ally none of the people buried in the Malmo¨ ceme- with age at death. People with symptoms died at tery had leprosy, this sample can be utilized for earlier ages than people without symptoms. The testing the assumption about conditioned indepen- relationship is statistically significant for all seven dence among the symptoms. It was possible to test symptoms, and the affected people died at younger 20 combinations of the seven symptoms. The esti- ages (Table 5). This means that there is evidence for mated coefficients of correlation ranged between selective mortality for the severity of leprosy in the Ϫ0.07 and ϩ0.57. Six of the correlation coefficients Odense lepers’ community. In accordance with Wood were statistically significant at the 0.05 level, and et al. (1992), this means that the point prevalence of these were all positive. It appears that the condi- leprosy at death (the disease frequency among the tioned independence assumption is not quite ful- skeletons of the sample) does not directly reflect the filled, but the magnitude of the correlation coeffi- prevalence of the disease in the once-living popula- cients indicates that only a minor part of the tion. The estimation of this statistic and other as- variation of one symptom could be explained by cor- pects of the epidemiological dynamics of leprosy in relation. In fact, the only really high correlation the Middle Ages fall outside of the scope of the coefficient (r ϭ 0.57) is between the alveolar process present paper, but they would provide logical next and the nasal spine, both of which have very high steps in the analysis of leprosy in Medieval South- specificities, of 0.985 and 0.976, respectively. This ern Scandinavia. means that the few skeletons showing both symptoms probably belonged to people who actually did ACKNOWLEDGMENTS suffer from leprosy. The second highest correlation This research was primarily financed by the Dan- (r ϭ 0.37) is between palate changes and subperios- ish Foundation for Basic Research through the Dan- teal exosteoses on the fibula. These two symptoms ish Center for Demographic Research. The registra- are the most unspecific symptoms and the symptoms tion of the Malmo¨ skeletons was carried out in most likely to be the result of nonspecific processes collaboration with Malmo¨ Museum. Ulla Freund is related to aging. This correlation is clearly not due gratefully acknowledged for her help defining the to the pathological processes of leprosy, so it is po- osteological scoring system on which this paper is tentially damaging for the model. Future work on based. refining the model will have to address this problem of the assumption of conditioned independence in a LITERATURE CITED more systematic way, but for the present the as- Andersen JG. 1969. Studies on the Medieval diagnosis of leprosy sumption does not appear to be violated in a way in Denmark. An osteoarchaeological, historical and clinical which would invalidate the results. study. Copenhagen: Costers Bogtrykkeri. PALEOPATHOLOGICAL DIAGNOSIS OF LEPROSY 387

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